Electron-discharge device



Nov. 1, 1927.

T. R- GRIFFITH ELECTRON DISCHARGE DEVICE Filed July?. 1925 Patented Nov.1, 1927.

UNITED STATES PATENT. OFFICE.

THOMAS E. GRIFFITH, OF DOVER, NEW JERSEY, ASSIGNOR TO BELL TELEPHONELAB- ORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

ELECTRON-DISCHARGE DEVICE.

Application filed July 7, 1925. Serial No. 41,941.

This invention relates to electron discharge devices and moreparticularly to such devices capable of handling high voltage.

The object of the invention is to prevent arcing between the electrodesdue to the large differences of potential between them.

This object is attained in an external anode device by providing aclosed tapered metal shield around the cathode supporting structure, theupper portion being fitted over the glass stem and the lower portioncarrying a ribbed metal insert. A plurality of supporting rods arerigidly held in the ribbed insert and support the helical wire grid. Theend of the cathode support within the helical grid is protected by ametal shield supported on the grid supporting rods to prevent any arcingpath between the anode and. the cathode support. This arrangement provides an easily assembled structure in which one electrode support formsa-sinooth metallic surface to completely shield another elec trodestructure from are discharges and corona effects.

Referring to the drawings Fig. 1 shows an electron discharge device witha part broken away to clearly illustrate the invention. Fig. 2 is across section of the grid support on the line 2-2 of Fig. 1. Fig. 3 is apartial view of a modified form of grid support and Fig. 4 is a modifiedcathode shield for a two electrode device.

The electron discharge device, shown in Fig. 1, consists of a cup-shapedmetal anode 10 which forms a part of the enclosing vessel and a glassportion 11 which is joined to the tapered end of the anode at 12. Aglass stem 13 is fused to the end of the glass portion 11 and projectswithin the enclosing vessel. A concentric tubular glass extension 14 isjoined to the inner end of the glass stem 13. A metallic collar 15 isfrictionally supported on the glass extension 14 by means oflongitudinal corrugations 16. This collar is provided with perforatedtabs through which the cathode supporting rods 17 extend. A spacingsleeve 18 and nuts 19 rigidly support the rods 17 from the collar. Ametallic heat radiating shield 20 is supported on the rods 17 andcompletely shields the glass extensions 14 from the excessive heatgenerated in the device. A metallic block 21 is supported on the ends ofthe rods 17 and carries a central supporting rod 22 and a pair ofthreaded connectors 23. These connectors are insulated from the metalbase by lavite insulating bushings 24. Supported from the end of the rod22 is a pair of molybdenum wire nests 25 which carry insulating inserts26, preferably of lavite. Molybdenum wire suspension hooks 27 aresupported in the lavite inserts and project toward the metallic block21. A tungsten filament 28 is strung between the threaded connectors 23and molybdenum hooks 27. A

length of braided copper conductor 29 is connected to the other end ofeach threaded connectors 23 by means of nuts 30, these lengths of braidbeing connected to copper leading-in wires 31.

Since the voltages applied to the anode are considerably higher than thevoltages applied to the cathode, this large difference of potentialcreates arcing paths between the anode and the sharp points of thevarious elements contained in the cathode structure, and results inpuncturing the glass and consequently destroying the tube. This effectis counteracted in accordance with this invention by a tapered metalshield 32, preferably of sheet molybdenum, which surrounds the cathodesupporting structure. One end of the shield is cylindrical in form andis pro-' vided with a series of slots 33 parallel with the edge of theshield. A number of longitudinal corrugations 34 between the slot 33 andthe edge of the shield provide clamping means whereby the shield may befrictionally supported from the glass stem 13. The tapered end of theshield 32 is provided with a corresponding tapered metal insert 35,having inwardly projecting longitudinal ribs or grooves 36. Intermediatethe ends of the insert 35 a portion of the grooves is cut out to formapertures 37. A plurality of ofmolybdenum rods 38 extend into thegrooves 36 between the Wall of the shield 32 and the insert 35 and areprovided with projections 39 which fit into the apertures 37. When thesupporting rods 38 are properly located in the grooves 36, the insert 35is wedged into the tapered end of the shield 32 and is spot welded orotherwise securely fastened to the shield. This provides an eflicientand easily assembled structure for the grid supporting rods. A helicalwire grid 40 surrounds the rods 38 and is concentric with 41 attached tothe shield 32 leading-in wire and 1s extends through glass tubulation 42sealed thereto at the outer end.

To prevent any injury to the lavite insulators on the cathode supportingstructure due to corona discharges from the anode, a molybdenum disc 43is welded to the grid supporting rods 38, thereby forming a shieldbetween the cathode support and the end of the anode.

Fig. 3 shows a modified form of support in which the shield 32 is weldedto a molybdenum ring 44 into which the grid supporting rods 45 arefastened in any suitable manner.

While the invention has been disclosed with respect to a three electrodedevice, it is apparent that. the features of the invention may beapplied to two electrode or rectifier devices. For instance, in Fig. 4the cathode shield 46 is formed of drawn molybdenum and is welded to anextension 47 on the supporting rod 22. This forms an umbrella type ofshield around the cathode supporting insulators and prevents any injuryto them due to arcs from the anode.

Vhat is claimed is:

1. An electron discharge device comprising an enclosing vessel having aglass portion and an anode portion, a reentrant stem on said glassportion, a tubular metal shield, engaging said stem, a metallic inserthaving longitudinal ribs, a plurality of. metallic rods projectingthrough said ribs, and an electrode carried by said rods.

2. An electron discharge device comprising an enclosing vessel having aglass portion and an anode portion, a reentrant stem on said glassportion, a tubular metal shield frictionally engaging said stem, ametallic insert within said shield, said insert having apcrtured groovesa plurality of metallic rods positioned in said grooves, each of saidrods having a bent portion projecting from said grooves, and a wirehelix supported by said rods.

3. An electron discharge device comprising an enclosing vessel having aglass portion and an anode portion, a reentrant stem on said glassportion, a concentric tubular extension on said stem, a supportprojecting within said anode from said extension. a cathode carriedthereby, a tubular metal member enclosing said support, and a controlelectrode supported from said member.

4. An electron discharge devicecomprising an enclosing vessel having aglass portion and an anode portion, a reentrant stern on said glassportion, a concentric tubular extension on said stem, a supportprojecting within said anode from said extension, a cathode carriedthereby, a tubular metal shield enclosing said support, a plurality ofmetal rods carried by said shield, a wire helix supported by said rodsand surrounding said cathode, and a metallic shield carried by saidrods.

In witness whereof, I hereunto subscribe my name this 6th day of July,A. D. 1925.

THOMAS R. GRIFFITH.

